1. Field of the Invention
The present invention relates generally to roller reamer tools useful in drilling of earth formations during exploration for and production of oil and natural gas; and, particularly to structure for mounting the roller cutters to the tool body.
2. Description of the Prior Art
Roller reamers are down-the-hole tools adapted to be placed in various positions in the drill string used to drill oil and gas wells. The roller reamers are used to ream the borehole to accurate gauge diameter; or are used as stabilizers to keep the drill string straight and centered in the borehole. The use of the tool in a particular application will dictate whether the tool is assembled with roller cutters having cutting teeth to actually ream the hole or with smooth faced rollers (cutters) to function as a stabilizer.
Generally, a roller reamer comprises a cylindrical body having upper and lower end portions, threaded for connection with adjacent drill string members, and an intermediate portion. The intermediate portion is generally larger in diameter than the end portions and contains a plurality of axially elongated pockets spaced about its periphery to receive the roller reamer cutter assemblies.
A roller reamer cutter assembly is disposed in each pocket and comprises a roller cutter mounted for rotation on a main pin. The pin is attached, by various means, within the cavity to the body. Predominantly, the ends of the main pin are fitted into mounting blocks which are then welded, pressed into mating pocket structure, or bolted to the body, or various combinations of these mounting techniques.
It is desirable to provide a roller reamer tool that is field serviceable so that roller cutters may be replaced when worn out. It is also desirable to reuse the bodies since they are a very costly item.
Further, it is desirable to support the rollers on the tool body in a manner that permits a selection of various radial locations so that a body and cutter assembly can be adjusted, within a limited range, to contact or ream holes of various gauges or diameters.
The desire to replace worn cutters and salvage the bodies or to vary the gauge diameter of the tool is indicated by a number of patents directed to removeable, replaceable mounting means for the roller reamer cutter assemblies. Many methods of removably attaching the cutter assemblies are costly or difficult to machine or damaging to the body, as when welds are removed. For ease of machining and reduced cost, providing cylindrical mounting blocks fitted into cylindrical bores or sockets in the body adjacent each end of the roller cutter pockets is beneficial.
Illustrative of the use of cylindrical mounting blocks are:
______________________________________ Garrett 4,182,425 Abegg 2,134,095 Catland 2,199,693 Catland 2,084,430 Garrett 4,261,426 Allison et al 4,262,760 ______________________________________
Garrett, U.S. Pat. No. 4,182,425, discloses cylindrical mounting blocks which are stepped on their sides and press-fit into mating bores in the body. These are additionally held in place by bolts. The reamer main pin upon which the roller cutter rotates is inserted into a bore in the mounting block and either welded or pinned to the mounting block to prevent its movement. Also disclosed are means for removal of the mounting blocks from the body.
After repeated installation and removal of the blocks to replace worn roller cutters, the blocks and the sockets become worn on their cylindrical sides resulting in loss of the interference fit. Thus, the blocks are retained primarily by the mounting bolts, which can become loose. There is then substantial risk of damage to the reamer which could become severe enough to cause loss of parts in the hole, necessitating a very costly and time-consuming fishing job to remove the lost parts from the borehole.
It is an object of the present invention to provide a roller reamer that is readily field serviceable.
Another object of the invention is to provide roller reamer mounting means that will assure positive retention of the roller cutter assemblies.
Another object of the invention is to provide a roller reamer mounting means that permits a single body to be used to ream boreholes to various gauge diameters.